Wound paper tubes, or cores, are widely used in industry for winding and supporting film, textile material, paper and the like. These tubes are typically spirally wound tubes, although convolute wound tubes are also used to achieve these functions. Winding apparatus used to support the tubes during winding and unwinding operations normally employ two independent chucks that grip the core at each of its opposed ends by means of various chuck systems.
For heavy duty uses, such as for winding and unwinding for newspaper and Rotogravure Printing, the tubes can be very long, for example, up to about 10 feet (3.08 m) for U.S. Rotogravure Printing and 10.5 feet (3.22 m) for European Rotogravure Printing. In view of the large size, these tubes must be very heavy and strong in order to be able to carry the weight of a large roll of paper. In addition, the ends of the tube which are engaged by various chuck systems must also be very strong in order to withstand the torque applied to the tube ends during the wind and unwind operations.
One common type of chuck employed in winding operations for paper is a splined chuck which supports the core axially and also functions to prevent the core from slipping on the chuck when torque is applied. Typically, these chucks have a frustoconical exterior shape and there are a plurality of circumferentially distributed, axially elongate splines on the outer surface of the chuck. The core is mounted onto the chuck by partial insertion of the chuck axially into the end of the paperboard core. The chuck is inserted into the core employing a predetermined amount of axial force so that the axially elongate splines on the face of the chuck are positively engaged with and embedded into the paperboard core end faces and the adjacent interior peripheral surfaces thereof.
Typically, the rotation of the roll of paper material is achieved by means of a drive roll which contacts the face of the paper roll for rotation thereof. During the winding and unwinding operations, the rolls of material are often subjected to substantial circumferential acceleration and deceleration by the winding machines. This, in turn, subjects the engaged ends of the paperboard roll to substantial torque forces. If the tube construction and the resultant strength thereof are deficient, the chuck engaged into the tube end can tear the paperboard materials, resulting in "chew-out" of the tube ends. In such event, the tube ends are no longer positively engaged by the splined chuck.
Various testing apparatus have been used by core manufacturers and users to evaluate various properties of tubular cores. For example, spiral delamination strength of tubular cores has been measured in the industry by employing metal end caps on the tubular cores together with special chucks which firmly hold the core in place during testing. An electric motor and speed reducing transmission apply torque to the core until the core spirally delaminates. This in turn allows both core manufacturers and core users to evaluate spiral delamination strength of the core.
However, spiral delamination strength is only one parameter of core strength. Typically, when paperboard cores are supported by splined chucks, the paper at the core/chuck interface will shear and the chucks will chew-out the core prior to a spiral delamination of the entire core. Thus, the "chew-out strength" is typically the limiting parameter for the amount of torque that can be applied to paperboard cores when mounted on splined chucks.
There is, however, no commercially available device for accurately testing the chew-out strength of paperboard cores. Thus, neither core manufacturers nor core users can accurately evaluate chew-out properties of paperboard cores other than by actual use of the paperboard cores in the manufacturing environment. As a result, it can be necessary for a manufacturer to over-design paperboard cores so that the chew-out strength is much greater than actually needed, on the one hand, while on the other hand, core users and purchasers cannot accurately evaluate a chew-out strength properties of cores prior to the actual use thereof.